Electrical neuromuscular stimulator for measuring muscle responses to electrical stimulation pulses

ABSTRACT

The electrical stimulator includes an electrical pulse generator arranged in a case, stimulation electrodes ( 7 ) to be placed on a user&#39;s skin on the motor points of the muscles to be stimulated, each electrode ( 7 ) being connected to an electric cable ( 5 ) connector, the other end of the cable being connected in a removable manner to a signal input and/or output socket of the case for receiving the electric pulses, at least one sensor ( 11 ) for measuring the muscle reactions caused by the electric pulses, and electronic means in the case for receiving the measurements from the sensor. The sensor ( 11 ) is intrinsically linked to one of the electrodes ( 7 ) or to the connector ( 6 ). At least one conductor wire ( 15 ) of the cable connects the electrode ( 7 ) independently of the sensor ( 11 ).  
     The stimulator finds application in particular in the field of sports for the passive exercising of muscles stimulated by electric pulses, or in the re-education of atrophied muscles. In this case, the sensor ( 11 ) is used to provide data as to the reactivity of the stimulated muscles and their fatigue level. This data is seen on a display of the stimulator and is used to adjust the stimulation parameters manually or automatically.

[0001] The invention concerns an electrical neuromuscular stimulator formeasuring muscle reactions generated by electrical stimulation pulses.The stimulator includes an electrical pulse generator arranged in acase, at least one pair of stimulation electrodes intended to be placedon the skin of an user in the vicinity of the motor points of themuscles to be stimulated, each electrode being connected to one end ofan electric cable, the other end of which is connected to the case toreceive the electric pulses from the generator, at least one sensorsensitive to the muscle reactions caused by the electric stimulationpulses and arranged for transmitting electric measuring signalsrepresentative of said muscle reactions to electronic means in thestimulator case.

[0002] The invention also concerns an electric cable and a stimulationelectrode for a neuromuscular electric stimulator.

[0003] The sensor supplies data regarding the useful muscle reactions inparticular in order to know the fatigue level of the electricallystimulated muscles. The measurements obtained from the sensor allow theparameters of the electric stimulation pulses to be adjusted eithermanually by viewing the shape of the signals received by the sensor on adisplay or automatically by adjusting the electric stimulationparameters as a function of the muscle fatigue. Adjusting the parametersconsists in correcting either the frequency of the pulses, or theamplitude or duration of the voltage or current pulses, or the durationof muscle contraction and relaxation, or the number ofcontraction/relaxation cycles, or any combination of the precedingparameters.

[0004] The object of electric stimulation or electrostimulation is tocontrol working of the muscles by the intermediary of electric voltageor current pulses as a function of programmed parameters. Each voltageor current pulse provides excitation of the nerve fibres which controlthe muscle fibres via the motor end-plate This excitation causes anelementary mechanical muscle response called a twitch with a duration ofthe order of 0.1 seconds.

[0005] The voltage or current pulse is repeated over time at anadjustable frequency. If this frequency is low, for example 10 Hz, theworking power of the muscles is slight, whereas for a high frequency,for example 100 Hz, the working power of the stimulated muscle fibres isvery high. This very high power corresponds to a powerful tetaniccontraction. The muscle fibre twitches can no longer be separated aftereach pulse at this high frequency, which means that a temporal summationof the twitches occurs which leads to a tetanic contraction.

[0006] If the stimulated muscles are stimulated at a high frequency,they will tend to become tired. In this case, the exercising sessionconsists in alternating contraction periods and rest periods. The restphase allows the fibres to relax and recover prior to the nextcontraction phase.

[0007] In the medical field, electric stimulators are used to assisthandicapped persons or accident victims so as to overcome deficienciesin muscular activity or to allow them to rehabilitate witheredmusculature. Electric current or voltage pulses are transmitted to saidmuscles via the electrodes placed on the skin or subcutaneously in orderto make them work passively. Measurements of the muscle reaction causedby the electrically evoked twitch allows the electric pulses to betransmitted to the electrodes to be adjusted as a function of the levelof the electrical or mechanical amplitude measured on the innervatedmuscles without thereby excessively tiring the muscles stimulated. Thisadjustment of the electrical parameters of the stimulator is used inparticular for handicapped persons or accident victims, to prevent thembeing continually obliged to ask for external help when they have tomove one or other of their deficient limbs.

[0008] A stimulator of this type is shown in U.S. Pat. No. 5,070,873which discloses a control loop for the electric pulses to be supplied tothe muscles to give them sufficient motricity. In a first phase,electromyographic sensors detect the voluntary muscle activity which inthe case of a handicapped person is lacking. The voltage measurementobtained by the sensors represents the low contraction state of theactivated muscles which leads to adjusting the electric pulses from thepulse generator to send voltage pulses adjusted to the expected reactionto the muscle motor nerves, in particular to allow automatism in thecoordination of movements desired by the handicapped person.

[0009] The electromyographic sensors can be separated from thestimulation electrodes, but may also be combined therewith. In thelatter case, a third electrode is necessary. If the same active surfaceof the electrode is used both as stimulation electrode and sensor, thisinvolves controlling, with difficulty, the signals originating from thesensor following the electric pulses sent across the electrode.

[0010] The combination of the sensor with the electrode requiresrectangular biphasic voltage pulses to be sent to perform themeasurements by the sensor. It is to be noted that in this case, forvoltage pulses, the stimulation current provided depends on theimpedance of the electrode and the skin. This impedance is not the samefrom one person to another, or can vary rapidly over time in the sameperson, which leads to different muscle reactions for identical voltagepulses sent to the electrodes.

[0011] The use of a current pulse generator allows one to be rid of thedrawbacks of a voltage pulse generator, since the pulse is kept constantwhatever the impedance of the skin and the electrode, and thus allowsthe same number of fibres recruited for stimulation to be maintained.

[0012] One drawback of this combination of active surfaces of the sensorand the electrode lies in the fact that after the sequence of sentbiphasic voltage pulses, there remains a residual voltage which can havea value of ten volts, whereas the measurement voltage drawn from themuscles by the sensor is of the order of a few millivolts. It is thusnecessary to attenuate this residual voltage in order to be able to makean accurate measurement in particularly of the fatigue level of thestimulated muscles. This is why sensors separated from the electrodesprovide better results than those combined as described hereinbefore.

[0013] French Patent No. FR 2 425 865 also discloses a bioelectricallycontrolled electric muscle stimulator. A carrier frequency generatorprovides an electric signal to the muscles to be stimulated which isadjusted as a function of the bioelectrical activity of the innervatedmuscles. With this adjustment of the electric pulses as a function ofthe measured muscle reaction, this stimulator offers a wide range ofuses. It allows, in particular, a certain motor automatism of movementsfor example during sports exercising or for assisting handicappedpersons.

[0014] The measurement sensors are of the electromyographical type andcan also be combined with the stimulation electrodes, but in this case,since the voltage pulses sent to the muscles are mainly voltages of thesinusoidal order, drawing the EMG signals originating from the samestimulation electrodes using filters does not pose too much of aproblem, which is not the case with rectangular voltage pulses.

[0015] The muscular contraction measurement means for providing data asto the state of reaction of the stimulated muscles can be performed inmany ways. The measurement can be either electrical usingelectromyographical sensors, or mechanical followed by an electricalconversion for example using acoustic sensors (microphones). Such anarrangement is shown in U.S. Pat. No. 4,805,636 in which the vibrationsof the contracting muscles are measured.

[0016] In this Patent document, two microphones are placed at differentlocations where the innervated muscles respond mechanically by a twitchto the voltage pulse generated by an electric pulse generator. Afeedback circuit takes account of the voltage signals given by the twomicrophones in order to adjust the twitch or the electric pulses whichthe generator generates for the muscles.

[0017] Strain gauges like any other type of electric conversionmechanical sensor can be used as described in U.S. Pat. No. 5,507,788.The strain gauges are used to measure a torque developed by thestimulated muscles. They are arranged at a distance from the stimulationelectrodes. The signals thereby obtained from the gauges are processedby a set of circuits in the stimulator in order to adjust thestimulation parameters of the pulse generator as a function inparticular of the muscle fatigue.

[0018] The use of strain gauges can only be applied in the case where itis possible to be able to measure a torque. A sensor of this type isnot, however, appropriate if measurements are made for dorsal orpectoral muscles for example, which do not involve movement of asegment.

[0019] One object of the invention is to use a structure combining astimulation electrode with a sensor for measuring muscle reactions whichovercomes the drawbacks of the stimulators described hereinbefore.

[0020] Another object of the invention consists in allowing an user tothink only of placing the electrodes on the muscles as for a standardelectric stimulator while in addition providing, via the sensorscombined with the respective electrodes, measurements of the musclereactions at the locations stimulated.

[0021] The objects of the invention are achieved as a result of thestimulator indicated hereinbefore which is characterised in that thesensor is mechanically connected to one of the electrodes or to the endof one of the cables on the electrode side, and in that at least oneconductor wire per electric cable connects the respective electrodeindependently of the sensor.

[0022] The objects of the invention are also achieved as a result of theelectric cable for a stimulator which is characterised in that one endof the cable on the electrode side has a connector for being connectedto the structure of a stimulation electrode via removable securing meansalso acting as an electric contact for the active surface or surfaces ofthe electrode, in that the connector includes at least one portion of amuscle reaction measurement sensor, and in that it includes in aninsulating sheath at least one conductor wire for connecting the activesurface or surfaces of the stimulation electrode independently of thesensor.

[0023] The objects of the invention are also achieved as a result of thestimulation electrode for a stimulator which is characterised in that itcomprises at least one conductive active surface for receiving theelectric pulses and in that the active surface is electrically connectedto removable securing means to a cable connector.

[0024] One advantage of the stimulator with the electrode and measuringsensor combination consists in facilitating the placing of said elementsfor example for the passive training of a sportsman using such astimulator or for all other applications. The sportsman knows where toplace the electrodes on the motor points of the muscles which he wishesto exercise. When first using such a stimulator, he has had to learn tosituate the motor points for the muscles to be exercised. Through habit,he easily knows how placing them at the desired locations and thusbeginning the exercising session.

[0025] The supplementary addition of a sensor with the electrode whichhe positions will not pose any additional problem. In addition tostimulation, he will be able to take account of the fatigue of thestimulated muscles for example on a display of the stimulator.

[0026] Likewise, if the stimulator includes means for receiving signalsfrom the sensor able to act on the pulse generator, the electric voltageor current pulses sent to the stimulation electrodes are automaticallyadjusted as a function of the muscle fatigue thereby avoiding anysubsequent handling by the user. The measurement signals transmittedfrom the sensor to the stimulation reception means either pass via adifferent conductor wire to the electrode conductor wire, insulated inthe electric cable sheath, or using signal transmitting means withoutany connecting wire.

[0027] One advantage of using a sensor of the electromyographical typeor with mechanical-electrical conversion of the accelerometric oracoustic type lies in the fact that they can be used for any muscle inthe body. Dorsal muscles are one of the examples of muscles in which thereaction measurement is not possible using a strain gauge sensor or moregenerally using a torque or force sensor.

[0028] Another advantage in the use of an electromyographical sensorwith an electrode consists in having two active surfaces, one for thesensor and the other for the electrode. Consequently, the muscleresponses are measured while minimising the disturbances originatingfrom the active surface of the stimulation electrode.

[0029] Another advantage of the stimulator according to the inventionconsists in minimising the number of electrodes combined with themeasuring sensors necessary on the one hand for stimulating the musclesand on the other hand for measuring the muscle reactions. One pair ofelectrodes combined with at least one sensor is sufficient to stimulatethe muscles at the desired locations and to provide data as to thereactions of the stimulated muscles. The conductor wires connecting thesensor and the respective electrode are regrouped in a single electriccable. The manufacturing costs are thus reduced to a minimum.

[0030] The objects, advantages and features of the stimulator willappear more clearly, in a non limiting manner, in the followingdescription of the different embodiments illustrated by the drawings, inwhich:

[0031]FIGS. 1a and 1 b show the stimulator before and after theconnection of the electric cables to the electrodes placed on a user'sskin,

[0032]FIG. 2 shows a partial cross-section of a first embodiment of anelectric cable connector with an integrated measuring sensor fixed ontoa stimulation electrode,

[0033]FIGS. 3a and 3 b show a partial vertical cross-section and abottom view of a second embodiment of an arrangement of anelectromyographical sensor and electrode,

[0034]FIG. 4 shows a partial cross-section of a third embodiment of anelectric cable connector with an integrated measuring sensor fixed to astimulation electrode, and

[0035]FIG. 5 shows diagrams of the electric signals sent to theelectrodes and the muscle response.

[0036] The stimulator described hereinafter relates preferably to astimulator used within the field of sport and re-education in whichmuscle stimulation is used to exercise them passively. Rectangularcurrent pulses are supplied to electrodes 7 placed on the skin at themotor points of the muscles to be stimulated. In response to thisstimulation, the muscles contract generating a mechanical twitch. Aspreviously described, current pulses have proved preferable to voltagepulses, since one is not dependent upon the variable impedance of theelectrode and the skin of the person using the stimulator.

[0037] Current pulses are supplied over time at a given frequency.According to the pulse repetition frequency, the muscles do not havetime to relax before the next pulse which increases the working power ofthe muscles, but on the other hand, they become tired. It is thusadvantageous to know the fatigue of the stimulated muscles in order toknow the state of the muscles being exercised and also to be able totake advantage of this measurement in order to adjust the stimulationparameters automatically.

[0038] In FIGS. 1a and 1 b, the stimulator is represented by a case 1enclosing in particular the current pulse generator and the means forreceiving the signals originating from the sensor. On said case 1,programme selection buttons 2 are used to select the desired exercisingmode as a function of the sport usually practised or the stimulationprogramme as a function of the pathological state (amyotrophy, hypotony,. . . ) of the muscle to be re-educated. The stimulator also includes avisual display device 3 for displaying in particular the programmesselected, the stimulation pulses, the muscle reaction measurementresponses, or even statistics for the exercising sessions. Display 3 isformed for example by a liquid crystal display.

[0039] One end 4 of a pair of electric cables 5 is connected in aremovable manner to one of the signal input and output sockets ofstimulator case 1. Other sockets for connecting the cable are accessiblefor connecting several pairs of electric cables 5. From the connectionto the corresponding socket, the two cables are joined so that they arenot twisted when stored. They are however separated over the second halfof the length of the cables so that their connector 6 can be fixed toseparated electrodes 7. The connectors have complementary means whichcan be fixed in a removable manner to studs 8 of electrode structure 7.

[0040] Muscle reaction measuring sensors, which are not visible in FIGS.1a and 1 b, are housed in electrode structure 7 or in connector 6. Thesensors are housed either in one of the electrodes or in one of theconnectors or in both. Measurement of the muscle reactions usuallyoccurs at the location where the current pulse reaches the electrodes,since the other electrode is used only for the return of the current.

[0041] A battery housed in the case supplies the stimulator with power,but it is also conceivable that the stimulator receives an externalvoltage supply through connection to the 220V or 110V mains supply via atransformer.

[0042] In FIG. 1a, the two connectors 6 are shown in a position at adistance from electrodes 7, since initially, the user places flexibleself-adhesive electrodes 7 with their active surface in contact with theskin generally on the motor points. In one embodiment, the self-adhesivesurrounds for example the active surface which occupies more than halfof the surface of the electrode structure.

[0043] Once the electrodes have been placed on the skin, connectors 6are fixed to electrodes 7, as can be seen in FIG. 1b. In thisembodiment, connectors 6 are mounted so as to rotate freely on studs 8.

[0044]FIG. 2 shows a first embodiment of the sensor assembly with thestimulation electrode. Sensor 11 is embedded in the body 18 of connector6 in the case in which it is obtained by moulding a plastic material. Inthe connector, just above complementary means 10 for the fixationthereof to stud 8 of the electrode, there is an acceleration meterforming sensor 11 arranged on a printed circuit 13 which includes allthe components 12 for amplifying and processing the acceleration metersignals. The acceleration obtained by the vibration of the stimulatedmuscles is of the order of several g.

[0045] Instead of acceleration meter 11, an acoustic sensor, such as amicrophone can be mounted on the printed circuit to perform musclereaction measurements.

[0046] At least two insulated conductor wires, preferably three wires 14are fixed onto metal pads of the printed circuit to bring on the onehand the electric power supply originating from the stimulator case tothe printed circuit components and on the other hand to send the musclevibration measurement signals to the stimulator case. Another insulatedconductor wire 15 is fixed to metal means 10 to bring the current pulsesto the electrode. All the insulated conductor wires 14 and 15 areenclosed in a sheath of an electric cable 5.

[0047] The electrode structure is composed of a base plane 17 made of aflexible insulating material, such as a fabric or an elastomer, able tomatch the shape onto which it is placed, for example a user's arm. Belowstructure 17, a conductive film is fixed, for example by bonding ordeposition of conductive particles, over a large portion of the surfaceof structure 17. This conductive film constitutes active surface 9 ofthe electrode via which the current pulses excite the motor-nerves ofthe muscles to be stimulated. Metal film 9 is connected through aconductive hole 16, in particular a metallised hole, made in structure17 to metal stud 8.

[0048] The contour of the active surface of electrode 9 is coated with aself-adhesive material or a self-adhesive film so as to be able to holdelectrode 7 on a user's skin. These electrodes are in principledisposable electrodes which can be used for one exercising session orfor several sessions.

[0049] In an alternative embodiment, the fixing of the connector to theelectrode structure via a snap fastener can be reversed by placingcomplementary means 10 on base plane 17 and stud 8 on connector 6.

[0050]FIGS. 3a and 3 b show a second embodiment of the electrode sensorassembly. The sensor used in this embodiment is of theelectromyographical type.

[0051] As in the first embodiment discussed hereinabove, connector 6which is obtained by plastic moulding 18 can include on the interiorthereof all the electronic components for processing the signalsoriginating from the EMG sensor, but in this variant of FIG. 3a, all theelectronic components are integrated in the stimulator case.

[0052] Connector 6 includes two metal pots 10 and 20 each connected, forexample by soldering, to the end of a respective insulated conductorwire 14 and 15, or conversely. The pots, in addition to a length of theconductor wires and the end of a flexible sleeve 19 of electric cable 5,are moulded in plastic material 18 of the connector.

[0053] Electric cable 5 encloses, in this case, only two insulatedconductor wires 14 and 15 in its insulating sheath.

[0054] The electrode structure includes, under base plane 17, a firstactive conductive surface 9 of the stimulation electrode and a secondactive conductive surface 11 which has no contact with the first activesurface forming the EMG sensor. The second active surface is placedbeside the first active surface. As shown in FIG. 3b, first activesurface 9 is made for example with a greater dimension than secondactive surface 11. Around the active surfaces, the base plane is coatedor covered with a self-adhesive material or film to keep it on theuser's skin without using other means.

[0055] In FIG. 3b, the shape of the active surfaces is approximatelyrectangular, but other embodiments are entirely conceivable, for examplehaving first active surface 9 in a circular shape placed at the centreof the electrode structure and the second active surface in the shape ofa ring placed coaxially to the first surface.

[0056] Each active surface 9 and 11 is connected, through conductiveholes 16, in particular metallised holes, to a corresponding metal stud8 and 21 situated on the other side of the base plane. Since these studs8 and 21 are chamfered on their top portion they are inserted with acertain mechanical resistance into metal pots 10 and 20 of the connectorto be held therein during use. The forced insertion into the metal potsusing chamfers for guiding assures a good electric contact for thetransmission of the current pulses to the electrode and the electricmeasurement of the muscle reactions. Of course, an arrangement as shownin FIG. 2 can also be applied in this second embodiment.

[0057] Several active surfaces 9 and 11, whether for electricstimulation or measurement, can be placed under base plane 17. Theactive stimulation or measuring surfaces are either all electricallyconnected at the surface of base plane 17 through metallised holes 16,or each connected to a corresponding stud. In the latter case, amultipolar connector has to be used.

[0058] The two studs 8 and 21, and the two metal pots 10 and 20 can bedesigned closer together, but this involves making metal conductors onbase plane 17 on the side of the connector connecting metallised holes16 with each of studs 8 and 21.

[0059] It is also conceivable to provide studs 8 and 21 on connector 6and metal pots 10 and 20 on base plane 17.

[0060] As previously, the electrodes have a flexible structure to matchthe surface of the skin on which they are placed, but there is nothingto prevent them having a rigid structure.

[0061]FIG. 4 shows a third embodiment with a sensor 11 which isidentical to that shown in FIG. 2. The elements which are the same asthose of FIG. 2 bear the same reference signs, and will not all beexplained again.

[0062] In this third embodiment, cable 5 includes only one conductorwire 15 in an insulating sheath for bringing the electric pulses to theelectrode. The measuring signals from sensor 11, processed orunprocessed in connector 6 are, however, sent by wireless measuringsignal transmitting means 22 via electromagnetic waves 23 or other wavesto electronic receiving means in the stimulator case. These transmittingmeans are placed on printed circuit 13 to receive the measuring signalsfrom sensor 11. Waves 23 picked up by the receiving means of the caseare converted into electric signals representing the measurement valuesof sensor 11 to be displayed on a display and/to adjust the stimulationparameters.

[0063] A power source for all the electronic components 11, 12 and 22 isprovided in connector 6 in the form of an electric battery 27. Thepositive and negative poles of battery 27 are in contact in a batteryhousing with a metal wall 24 for one of the poles and with a metal base25 for the other pole. The battery is kept in its housing by a plug 26pressing the battery 27 against its contacts 24 and 25. This plug 26 iseither screwed in, driven by force, or soldered.

[0064] Plug 26 could also be omitted, if the battery in its housing wasembedded in the body of connector 6, in the event that it were notdeemed necessary to change it when it becomes flat.

[0065] The connector is mounted in a removable manner on the electrodestructures whether in the first, second or third embodiments to allowthe user to first place the electrodes at the selected locations withoutbeing inconvenienced by the electric cables. The connector could also beintegral with the electrode structure.

[0066] The means for fixing the connector to the respective electrodecan take various other forms than those mentioned previously. One canenvisage fixing means using a magnet housed either in the connector, oron the electrode structure, and a metal part placed either on theelectrode structure or on the connector. This fixing arrangement has toguarantee the contact between metal pads between the two elements forsupplying electric pulses or also for the sensor measurement.

[0067]FIG. 5 shows by way of illustration three diagrams of the signalsreaching the stimulation electrodes and those drawn from the musclereaction or response measurement whether by an acceleration meter (VMG)or an electromyographical sensor (EMG).

[0068] A current pulse is first imposed on the stimulation electrode.This pulse can be monophase, but is preferably biphase as shown in FIG.5.

[0069] The maximum amplitude of the current IA is graduated from 0 to120 mA. The higher this amplitude, the higher the number of musclefibres recruited. This thus corresponds to the spatial recruitment ofthe fibres which perform the work required by the selected programme.

[0070] The second diagram of FIG. 5 shows the schematic shape of theskin electrode voltage. This voltage passes through a maximum value Vmaxof around 100 V and a minimum value of −10 V. After the current pulsehas returned to 0, there remains a residual voltage Vres of severalvolts across the electrodes, which is why it is difficult to use thesame active surface to measure the stimulated muscle reaction voltagevariations using an EMG sensor, since the voltage measured by the sensorVmes is of the order of a few millivolts.

[0071] The variations in voltage due to the muscle vibrations andmeasured by the acceleration meter (several g) and the EMG sensor forlow frequency current pulses are shown in the third diagram.

[0072] At higher frequency pulses, when the muscle is contracted, theacceleration meter provides a signal only during the initial and finalphases of the contraction. Conversely, the EMG sensor gives a signaleven during the muscle contraction phase.

[0073] Thus, in order to obtain measurements using an accelerationmeter, the acceleration signal generated can be measured either by oneor more muscle twitches between the muscle contraction periods, or bythe initial or final phase of the muscle contraction.

[0074] For a strength programme, the frequency of the pulses is high,whereas for an endurance programme, this frequency is low. It should benoted that for slow muscle fibres, the frequency is 30 Hz, whereas forfast muscle fibres, it is 60 Hz.

[0075] Following the description which has just been given, severalother alternative embodiments of a stimulator combining an electrodewith a measuring sensor can be envisaged within the reach of thoseskilled in the art without departing from the scope of the invention.

What is claimed is:
 1. An electrical neuromuscular stimulator formeasuring muscle reactions generated by electrical stimulation pulses,including an electrical pulse generator arranged in a case of thestimulator, at least one pair of stimulation electrodes intended to beplaced on an user's skin on the motor points of the muscles to bestimulated, each electrode being connected to one end of an electriccable, the other end of which is connected to the case to receive theelectric pulses from the generator, at least one sensor sensitive to themuscle reactions caused by the electric stimulation signals and arrangedfor transmitting electric measuring signals representative of saidmuscle reactions to electronic means in the stimulator case, wherein thesensor is mechanically connected to one of the electrodes or to the endof one of the cables on the electrode side, and wherein at least oneconductor wire per electric cable connects the respective electrodeindependently of the sensor.
 2. A stimulator according to claim 1,wherein each end of the electric cables on the electrode side issecurely fixed to the respective electrode structure.
 3. A stimulatoraccording to claim 1, wherein each cable end on the electrode side has aconnector connected to the respective electrode structure by removablefixing means.
 4. A stimulator according to claim 3, wherein theremovable fixing means are of the snap fastening type also acting aselectric contact between the connector and at least one activeconducting surface of the respective electrode.
 5. A stimulatoraccording to claim 3, wherein the removable fixing means, acting also aselectric contact between the connector and at least two active surfacesof the electrode, include at least two conductive studs inserted with acertain mechanical resistance in two conductive pots, the studs formingpart of the electrode structure and the pots forming part of theconnector, or vice versa.
 6. A stimulator according to claim 1, whereinthe measuring sensor is an electromyographical sensor having at leastone active conductive surface placed without electric contact beside atleast one other active conductive surface of the electrode receiving theelectric pulses, said active surfaces being placed on the motor pointsof the muscles to be stimulated.
 7. A stimulator according to claim 1,wherein the sensor is an acceleration meter or a microphone integratedin the connector of the end of the cable on the electrode side or in thestructure of one of the respective electrodes.
 8. A stimulator accordingto one of claims 6 and 7, wherein the means for processing the signalsreceived from the sensor are integrated in the connector or in theelectrode structure.
 9. A stimulator according to claim 1, wherein thesensor is in communication with the electronic means of the stimulatorvia wireless signal transmitting and/or receiving means housed in thecable connector or in the electrode structure, or via at least oneconductor wire of the cable other than that of the electrode.
 10. Astimulator according to claim 9, wherein an electric power source ishoused in the connector or in the electrode structure for supplyingpower to the electronic components for measuring muscle reactions.
 11. Astimulator according to claim 1, wherein it includes, on the case, avisual display device capable of displaying in particular electricstimulation programmes and data relating to the electric muscle reactionmeasuring signals.
 12. An electric cable for a stimulator according toclaim 1, wherein one end of the cable on the electrode side has aconnector for connection to the structure of a stimulation electrode viaremovable fixing means also acting as electric contact for the activesurface or surfaces of the electrode, wherein the connector includes atleast a part of a sensor sensitive to muscle reactions, and wherein itincludes in an insulating sheath at least one conductor wire forconnecting the active surface or surfaces of the stimulation electrodeindependently of the sensor.
 13. An electric cable according to claim12, wherein the connector encloses processing means for the signalssupplied by the sensor.
 14. An electric cable according to claim 12,wherein the means for fixing to the electrode are of the snap fasteningtype or of the multicontact type.
 15. An electric cable according toclaim 12, wherein the connector includes wireless signal transmittingand/or receiving means, and an electric power source for the electroniccomponents for measuring the muscle reactions.
 16. A stimulationelectrode for a stimulator according to claim 1, wherein it includes atleast one active conductive surface for receiving the electric pulses,and wherein the active surface is electrically connected to removablemeans for fixing to a cable connector.
 17. A stimulation electrodeaccording to claim 16, wherein it includes an electromyographical sensorhaving at least one other active conductive surface arranged withoutelectric contact beside the active surface receiving the electricpulses, or an acceleration meter or a microphone placed on the electrodestructure.
 18. A stimulation electrode according to claim 16, whereinits structure is flexible so as to be able to match the shape onto whichit is placed, and wherein a portion of its structure, surrounding theactive surface or surfaces in the form of a metal wire, is coated orcovered with a self-adhesive material or film so as to be able to stayon the skin without using additional holding elements.